This invention relates to a temperature-detecting element for detecting a mean temperature in a given region or abnormal local temperature changes therein.
Where the mean temperature of a given region is measured, for example, where the mean atmospheric temperature is determined to define the coefficient of through heat transfer of structural material in order to evaluate the physical properties of said structural material, then customary practice is to measure temperatures at a plurality of sites within said region and average the measured values to provide a mean temperature. Abnormal local temperature rise or fall in a region resulting from, for example, occurrence of a fire, leakage of molten metal from an electric furnace, damage or corrosion of the interior material of a reactor or gas leakage from an LNG tank is determined likewise by measuring temperatures at a plurality of sites within the region and comparing the measured values.
To date, measurement of temperatures at a plurality of (for example, an n number of ) sites has been effected by setting an n number of, for example, thermocouples, thermistors, electric-resistance thermometers or mercury thermometers at said sites.
If a thermocouple, a thermistor, or an electric-resistance thermometer is to be used as a temperature-detecting element, a total of 2n number of lead wires have to be provided for the temperature-detecting elements set at n number of sites. As the sites of measurement increase in number, the lead wires intricately intersect each other, presenting difficulties in their connection or probably giving rise to errors in said connection. Further, it is necessary to install an n number of meters to find measured values of temperature or a multicircuit changeover switch, presenting considerable inconvenience in practical application. Particularly application of a thermally sensitive resistor as a temperature detecting element is accompanied with the disadvantage of providing an external constant voltage power source. Where a mercury thermometer is used, a temperature-measuring worker must have an access to each site of measurement to find a measured value of temperature thereof. Particularly, where the worker has to measure the temperature of the open air, his access to a given site appreciably affects the temperature of said site, failing to carry out an accurate measurement.
A recent improved thermocouple consists of a multi-junction type in which one of the metal wires constituting a thermocouple is used as a common conductor. Even this improvement only has the effect of decreasing the number of metal wires from 2n to (n + 1), little contributing to the resolution of other problems referred to above.
Further where measurement is made of the temperature of the surface of an object, a scanning type infrared thermometer or infrared camera is used. However, such temperature determining device is expensive, demands a considerable skill of an operator, and is moreover accompanied with the disadvantage of requiring an operator to judge the result of detection by the naked eye on the screen.